The present invention is generally related to washing machines, and more particularly to a method and apparatus to reduce displacement of the wash basket that occurs at the beginning of a normal spin cycle during speed ramp up.
A common problem with washing machines, whether a horizontal axis, vertical axis, or tilt axis machine, is that the wash basket or rotary washing element of the machine experiences single unbalanced or single off balance load conditions during a wash cycle that affect rotation. The single unbalanced load condition is typically caused by an uneven distribution of laundry within the spinning wash basket. When the laundry within the wash basket is wet, it is relatively heavy which exaggerates any unbalanced condition. Rotation of the wash basket that carries an unbalanced or unevenly distributed load of laundry causes lateral displacement and vibration. Lateral displacement during the spin cycle is undesirable for a number of reasons including movement of the washing machine, noise, and premature wear and tear of washing machine components.
Many washing machines include an annular balancing ring that is mounted to the wash basket in order to reduce the amount of displacement during the spin cycle. A large component of a basket displacement occurs during speed and acceleration or ramp-up to the high-speed spin speed. Balancing rings are typically only designed to assist in correcting an unbalanced condition in a washing machine after the wash basket has reached full speed during the spin cycle.
One problem with conventional balancing rings is that the balancing mass providing the weight distribution correction actually adds to the unbalance of the wash basket prior to attaining a rotational speed that is greater than its present vibration frequencies. Attempts have been made to reduce the effects of this preliminary unbalanced phase of the ramp-up speed during the spin cycle.
European patent document EPO 787 847 A2 of Noguchi, et al discloses using a fluid balancing ring on a horizontal axis washing machine wherein the rotational speed of the fluid balancer is stepped-up from a first lower speed to a second higher speed in order to reduce the effects of the initial unbalance. Noguchi, et al this closes during a first lower rotational speed for a fixed time period and then ramping this speed up to the normal spin cycle speed. This first lower speed is run at a speed that is higher than the critical or resonance rotational speed of the fluid balancer, but lower than the critical or resonance rotational speed of the wash basket suspension system. Noguchi, et al does not address use of a ball balancer and further does not address the speed of the wash basket as it passes through the critical speed range of the suspension system.
U.S. Pat. No. 5,862,553 to Haberl et al. discloses a horizontal axis washing machine that uses a ball balancing ring for correcting imbalance in a rotating wash basket of the machine. Haberl et al. also discloses ramping up the rotation speed and specifically addresses the effect of gravity on the load within the horizontal axis washer. Haberl et al. attempts to compensate for the effect of gravity. In doing so, Haberl et al. initially drives the drum or wash basket and a continuous, relatively low, but variable speed wherein the speed variations are used to compensate for the effects of gravity on the unbalance of the wash basket. In horizontal axis washing machines, the unbalanced or heavy side of the wash basket speeds up by force of gravity as it falls and slows down by force of gravity as it climbs. The speed variation at the low speed of Haberl et al. attempts to compensate for this phenomenon.
Haberl et al. also discloses running the initial lower start up speed at a speed less than the speed at which resonance frequency of the wash basket occurs. Haberl et al. does not disclose addressing a particular resonance frequency for the suspension system for the wash basket.
One object of the present invention is to provide a method of reducing the effects of a single unbalanced or single off balance load condition in a wash basket having a balancing device during ramp up to a high-speed spin cycle. Another object of the present invention is to provide a method that reduces wash basket displacement during start up of the washing machine spin cycle. The further object of the present invention is to provide such a method for reducing this displacement during speed ramp-up that is equally useful for horizontal axis, vertical axis and tilt axis washing machines.
A still further object of the present invention is to provide such a method of reducing displacement of the wash basket during ramp-up of the high-speed spin cycle that particularly addresses large displacement of the wash basket caused by suspension system resonance. Another object of the present invention is to provide such a method of reducing displacement of a wash basket that is tuned to reduce the effects of cross over from a speed prior to reaching critical resonance frequencies of the wash basket suspension system to a speed that is above the these critical resonance frequencies. A further object of the present invention is to provide a suspension system that tunes the critical resonance frequencies to coincide with motor rotation speed in order to reduce the effect of the critical resonance frequencies on wash basket displacement.
These and other objects, features and advantages of the invention are provided by the method and apparatus disclosed herein. In one embodiment, a method is provided for reducing displacement of a wash basket of a washing machine that is rotatable about an axis of rotation within the machine. The washing machine has a drive motor that rotates the wash basket. The method includes attaching a balancing ring to the wash basket in a plane generally perpendicular to the rotation axis. The balancing ring has a balancing mass that is movable relative to the ring. The wash basket is then supported by a suspension structure to the washing machine. A resonance critical frequency is determined for each of two translational degrees of freedom that are in the plane of the balancing ring. Three other resonance frequencies are then determined for the three rotational degrees of freedom of the suspension structure. The suspension structure is tuned so that the two critical resonance frequencies of translation each occur at or below a critical first speed of the motor. The suspension structure is also tuned so that the three other frequencies of the rotational degrees of freedom occur at a second motor speed that is above the critical first speed. The motor is initially ramped up to an initial spin speed for rotating the wash basket wherein the initial spin speed is incrementally higher than the first critical motor speed and lower than the second motor speed. The motor is then held for a time period at the initial spin speed until the balancing mass moves relative to the ring to a correcting position opposite any imbalance of the wash basket. The motor is then finally ramped up to a final spin speed that is above the second motor speed for rotating the wash basket at the final spin speed.
In one embodiment, the method further includes ramping up the motor at a rate that permits the balancing mass to remain in the same correcting position relative to the balancing ring during ramp up and after reaching the steady state final spin speed.
In another embodiment of the invention, a washing machine includes a wash basket for rotation about an axis relative to the machine. A drive motor is mounted to the machine for rotating the wash basket. An annular balancing ring is mounted for rotation with the wash basket in a plane generally perpendicular to the rotation axis and has a balancing mass that is movable relative to the balancing ring. A suspension structure is mounted to the washing machine and supports the wash basket. The suspension structure has two critical resonance frequencies, one for each of two translational degrees of freedom of the suspension structure that lie in the plane of the balancing ring. The two critical resonance frequencies each occur at or below a first critical speed of the motor. The suspension structure also has three other resonance frequencies one for each of three rotational degrees of freedom of the suspension structure. Each of the three other resonance frequencies occur at or above a second motor speed that is higher than the first critical speed. The machine has the motor controller that can initially ramped up the motor to an initial spin speed that is incrementally higher than the first critical speed and lower than the second speed of the motor. The controller can dwell the motor at the initial spin speed at least until the balancing mass of the balancing ring is repositioned and stabilized to correct any imbalance in the wash basket. The motor controller can then ramp up the motor to a final spin speed that is higher than the second speed.
In one embodiment, The motor controller of the washing machine can ramped-up the motor at a rate that permits the balancing mass to remain in the same correcting position relative to the balancing ring while ramping up and after reaching the steady state final spin speed.
In each embodiment of the method and the apparatus, the axis of rotation may either be a vertical axis of a vertical axis washing machine, can be a horizontal axis of a horizontal axis washing machine, or can be a tilted axis of a tilted axis machine.
The present invention is directed to specifically tuned suspension structure for the wash basket wherein the translational resonance frequencies of two translational degrees of freedom that lie in the plane of the balancing ring occur at lower motor speeds than all three of the resonance frequency for the three rotational degrees of the system. The present invention also includes ramping up the speed of the wash tub to speed that is incrementally higher than the highest occurring motor speed of the two translational resonance frequencies but below the occurring motor speed for all three of the rotational resonance frequencies. By doing so, the balancing mass will shift from being disposed on the same side of the axis of rotation as an out of balance or heavy side of the wash basket, where it adds to the instability of the wash basket, to the opposite side of the rotational axis relative to the heavy side where it will reduce the imbalance. This transition typically occurs above both of the translational resonance frequencies for the two degrees of freedom that lie in the plane of the balancing ring. The present invention therefore reduces the amount of basket displacement, shaking, noise and vibration caused by the initial low rpm out of balance of most washing machines.
These and other objects, features and advantages of the present invention will become apparent upon reviewing the written description and the accompanying drawings. The foregoing and other objects of the invention are attained by the method and apparatus described herein that provide reduced displacement caused by an unbalanced load during start up of a wash basket in a washing machine during a spin cycle.